1. Field of the Invention
The present invention relates in general to a turbomachinery of a centrifugal or mixed flow type for use in fluid pumps, gaseous blowers and compressors, and relates in particular to a turbomachinery having inlet guide vanes and diffuser vanes.
2. Description of the Related Art
When a centrifugal or mixed flow pump is operated below the design flow rate of the pump, flow separation occurs in the impeller, diffusers and other components in the pump, thus lowering the operating efficiency of the pump to a value below its design efficiency. To overcome such problems, it has been a practice to provide variable-angle inlet guide vanes and diffuser guide vanes to adjust the vanes to suit the fluid flow pattern.
Typical examples of prior art references are: Japanese Patent Publication, H4-18158; Japanese Patent Publication, H4-18159; Japanese Laid-open Patent Publication, S63-239398; Japanese Laid-open Patent Publication, S63-230999; Japanese Laid-open Patent Publication, S55-107097.
In the above-mentioned method, controlling of the turbomachinery was conducted basically to adjust the diffuser vanes with the flow direction at the exit of the impeller for improving the performance and especially for avoiding the instability phenomenon at a low flow rate region. This was commonly acknowledged for a turbomachinery having diffuser vanes of conventional size and configuration.
However, the inventors have developed a novel diffuser vanes having novel configuration, and found that, at a higher flow rate region than a design flow rate, a higher performance of the turbomachinery is obtainable by using a novel control method different from the conventional one.
Further, in the conventional art described above, to control the angle of the diffuser vanes to suit an operating condition of the pump, it is necessary beforehand to accurately estimate the flow pattern from the impeller. Furthermore, for those pumps having inlet guide vanes, every time the setting angle of the guide vane is adjusted, the flow pattern of the fluid from the impeller changes for each setting angle of the guide vanes. It follows therefore that it is necessary to know beforehand, the performance characteristics of the pump for each setting angle of the guide vane.
In the conventional technologies mentioned above, it is necessary to perform tests for each angle of the inlet guide vane, by assigning a certain setting angle to the diffuser vanes and operate the pump on the basis of the experimentally obtained data. This approach presented a problem that the control technique is complex, and required an expenditure of high capital cost for the equipment as well as for the development of control programs. Additional problem is that it takes much time until a system is operated automatically at their optimum setting angles for the vanes.
A method for calculating the flow angle from the impeller exit is disclosed in a Japanese Laid-open Patent Publication, H4-81598, but this method involves several defects such that it includes several assumptions regarding the flow angle, that, because the flow pattern is distorted at the impeller exit in general, the calculation of flow angle based on the static pressure on the wall surface is questionable, and that, in the region of a flow instability, the precision of the computed results is also questionable.
There is a method in which pressure holes are provided on the diffuser vanes to measure the pressure so as to compute the direction of the flow from the impeller exit, as disclosed for example in a Japanese Laid-open Patent Publication, S57-56699, but this method is unsuitable for diffusers having thin vanes, and additional cost of fabrication of the holes is high.
A technique for measuring the wall pressure on the pressure side and suction side of the diffuser vanes has been disclosed in a Japanese Laid-open Patent Publication, S62-51794, but because the hole is provided on the wall surface of the diffuser, changes in the relative location of the holes, when the diffuser vanes are rotated, made it impossible to measure the pressure when a pressure hole becomes hidden by the diffuser vanes.
Furthermore, when the setting angles of the inlet guide vanes and diffuser vanes are adjusted, the pump performance can be altered significantly; therefore, unless the flow angle from the impeller is already known, it has been necessary to perform detailed performance tests for each setting angle of the guide vanes, and to determine the setting angles for the guide vanes and diffuser vanes based on these test results.
To control the pump automatically using the above method, it has been necessary to change the setting angles at least three times for testing (see for example, a Japanese Patent Publication, H4-18158, and a Japanese Patent Publication, H4-18159) to assess the characteristics of the pump in a particular operating situation, before the setting angle of the guide vanes and diffuser vanes can be selected. This methodology is time-consuming, and in particular, the method is unsuitable when it is necessary to decide the changes instantaneously, which would be the situation near a surge point.
The control methodology is even more difficult if the rotational speed of the pump is to be adjusted. Such an approach requires an advanced control facility, and the equipment and control programs becomes expensive.
A method to determine the angle of the diffuser vane from measurements of pressures existing at pressure holes fabricated on the surface of the diffuser vanes is disclosed in a Japanese Patent Publication, S57-56699, but the flow pattern of the flow from the impeller exit changes greatly in the width direction of the diffuser vanes depending on the operating condition of the pump, and therefore, if the measurements are taken only at the pressure holes located in the center region of the diffuser vanes, the deduced flow angles tended to be highly erroneous.
Further, because the pressure holes are located on the surface of the diffuser vanes, the total pressure is measured unexpectedly, and, in case of the machine handling high speed flow, the pressure level is generally larger than the static pressure, then, it is necessary to provide a high-range pressure gages, and therefore the precision of measured data is inadequate. Also, this method is not suitable for vanes having thin vane thickness, and the cost is high.